It's becoming well known that the 2.4 Ghz radios may be susceptable to undervoltage issues on the receiver battery supply. And, these have resulted in loss of control of the model. Spektrum did do some software updates a while back to reduce the time of "Rebooting" in case of a low battery issue. My testing on updated AR7000 receivers shows this "rebooting time" is less than a second.

IMHO, this is not a receiver issue, it's a problem with the receiver battery selected. By actual test, I've measured the peak currents pulled by all 7 Hitec 645MG in my giant scale Extra 330 model. That peak current was measured at 14 amperes, with the one millisecond peak holding feature of my Fluke 87V digital multimeter.

So, to illustrate this issue, two discharge current tests of 12 amperes were applied to a new LiFe 3200 Mah battery, and to a new 5 cell 2700 Mah Nih "AA" type receiver battery.

The attached graph, taken from my Western Mountain CBAIII battery test unit shows it all.

Take a look at the attached JPG: The 12 Amp load on the Nih battery was shut off when the voltage dropped to 3.6 VDC, a value reached in about 2 seconds. Note that those Spektrum receivers will reboot when the receiver battery voltage hits 3.2 VDC. The Nih battery test was conducted immediately after it was fully charged. The results will be worse after a few flights on the model.

Again, IMHO, the 2.4 Ghz receiver of any large model with more than 4 servos and a receiver battery should be using a higher powered receiver battery than those "AA" type units. Recommendations would be one of those LiFe types, a "Sub C" 5 cell Nih battery, or a uBEC such as Castle Creations 10 (or 20) Amp Switching Battery Elimination Circuit.

This is a very good thread. It nice to see that an insufficient battery can be the root of these problems that many would say was the fault of the "Spectrum System". I have read numerous threads of problems that are Spectrum related, and thats where the blame is placed.

I on the other hand know from experience that, one crash I had was caused by a bad battery causing my rx to reboot(before the quicker reboot rx's), too low to the ground and smacking my heli hard. All my other crashes could be traced to pilot error and or battery issues.

Great stuff Denny. I too am a BIG fan of the LiFe packs for direct power on larger models. Add to this the power hungry nature of digital servos and the power requirements can be a bit stunning.

I have also found the RX's can boot at above 3.2v and think 3.5v is the real number (I think it is for Hitec stuff anyway!). So really 4v is the danger zone IMHO.

Makes one really wonder when servos became such power hogs. I guess it is when the got ultra powerful. I remember the days of flying .60 size glow models with one aileron servo that had 37in/oz of torque. I never seemed to need more then......

When you have any loads such as servos that draw high current, the safest way is to separate servo power from receiver power. Just use any small capacity battery (the current drain is very low) to power only the receiver and then power the servos with a separate bus. Now, even if you get a momentary voltage drop on the servo bus, the receiver keeps on chirping happily along and you will never suffer a brown out.

Great stuff Denny. I too am a BIG fan of the LiFe packs for direct power on larger models. Add to this the power hungry nature of digital servos and the power requirements can be a bit stunning.

I have also found the RX's can boot at above 3.2v and think 3.5v is the real number (I think it is for Hitec stuff anyway!). So really 4v is the danger zone IMHO.

Makes one really wonder when servos became such power hogs. I guess it is when the got ultra powerful. I remember the days of flying .60 size glow models with one aileron servo that had 37in/oz of torque. I never seemed to need more then......

A fantastic reminder of how important proper power is to our systems.

Mike

Hi Mike
I did check several of my Spektrum AR7000 receivers for undervoltage lockout on my variable DC supply. All were 3.2 volts DC plus or minus a little bit.

It's interesting that you've found that Hitec has a little higher undervoltage lock out level.

That 14 Amps measured on my 7 Hitec 645MG servos was measured by moving the transmitter sticks back and forth "Wildly". Perhaps this is not reasonable, but has anyone watched the rudder/elevator/ailerons of a large model airplane doing 3D or hovering?

When you have any loads such as servos that draw high current, the safest way is to separate servo power from receiver power. Just use any small capacity battery (the current drain is very low) to power only the receiver and then power the servos with a separate bus. Now, even if you get a momentary voltage drop on the servo bus, the receiver keeps on chirping happily along and you will never suffer a brown out.

Good point
I've noted the giant scale flyers in my club use those "Breakout" units that easily allows the separation of the receiver and servo battery circuits, along with dual batteries for redundant operation. One of the club members has a model with four 200 inch ounce servos powering just the rudder.

Denny - maybe my recollection was 3.5v was the safe level for Spekky stuff. I had a lock-out with my A9/Optima 7 Hitec stuff that cost me a $1k plane. I was foolish and used the ICE 75 BEC on 4 digital servos.

I should have used a 2s LiFe pack and I would still be flying that plane. I had the ICE BEC set at 6v output and alarm at 5.8v and it would kick off periodically and I didn't do anything! A .2v drop sure indicates the BEC is not keeping up. Not sure where the reboot voltage was but I was on final approach and the plane just kept flying right into our trees at the end of the runway.

I had plenty of warnings including guys going don't trust the ICE BEC but I didn't listen to them or my system when it kicked off the alarm. Pretty stupid eh?

Lesson learned. LiFe or separate BEC for all 4s planes and up for me now. My new large 6s Telemaster Plus actually has one 2s 640 mAh pack for just the SPC and a Castle 10amp BEC for the 6 analog servos. I will likely replace the BEC with a 2100 LiFe pack soon.

Thanks for the useful information! What is the advantage of LiFe compared to nano-tech LiPo?

Voltage.

LiFe is 3.6v per cell not the 4.2v per cell of the LiPo batteries. the LiFe quickly drops and holds around 3.3v/cell and that is PERFECT voltage for our receivers since a 2s pack will be right at 6.6v almost exactly that of a 5 cell NiCad/NiMh pack.

So the huge advantage is the pack needs no regulator*!

Cool eh?

* = no regulator if your servo's can handle that voltage, most will but a few do not.

Is it possible to separate the servo bus from the Rx power bus on receivers that are not set up that way from the beginning? Is this possible on something like the AR7000?

Yup, anythings possible, but something that would not be recommended. These radio control systems use something called double sided circuit boards with copper foil on both sides of the circuit board.

Trying to cut the proper foil pattern could be impossible, because the foil that would have to be cut might be under some component.

Much better to use one of those "breakout" panels made for this purpose. Not certain of the exact description of those panels, or a name of a supplier of these units. Several of my club members that fly giant scale models with twin cylinder engines over 100 cc use them exclusively.

Can any wattflyer readers provide more information on those "Breakout" panels, and what they are called, and who makes them???

Denny - maybe my recollection was 3.5v was the safe level for Spekky stuff. I had a lock-out with my A9/Optima 7 Hitec stuff that cost me a $1k plane. I was foolish and used the ICE 75 BEC on 4 digital servos.

I should have used a 2s LiFe pack and I would still be flying that plane. I had the ICE BEC set at 6v output and alarm at 5.8v and it would kick off periodically and I didn't do anything! A .2v drop sure indicates the BEC is not keeping up. Not sure where the reboot voltage was but I was on final approach and the plane just kept flying right into our trees at the end of the runway.

I had plenty of warnings including guys going don't trust the ICE BEC but I didn't listen to them or my system when it kicked off the alarm. Pretty stupid eh?

Lesson learned. LiFe or separate BEC for all 4s planes and up for me now. My new large 6s Telemaster Plus actually has one 2s 640 mAh pack for just the SPC and a Castle 10amp BEC for the 6 analog servos. I will likely replace the BEC with a 2100 LiFe pack soon.

Mike

Mike

Hi Mike
I've been flying my giant scale Extra 330 now for some 38 flights with a CC 10 Amp uBEC for primary receiver power, and a two cell 2300 Mah A123 battery with a series diode for backup power. The two supplies plug into the standard battery input, and the gear input of the AR7000 receiver for dual inputs to the receiver.

Much better to use one of those "breakout" panels made for this purpose. Not certain of the exact description of those panels, or a name of a supplier of these units. Several of my club members that fly giant scale models with twin cylinder engines over 100 cc use them exclusively.

Can any wattflyer readers provide more information on those "Breakout" panels, and what they are called, and who makes them???

I don't use them on any of the 50cc planes, and didn't go to one on the 111cc plane (36% Katana) as I don't have digital servos, and run an AR 9100 reciever that has redundant power feeds built in.

Ah Ha, thanks!

One of our old club members (Been flying RC since 1959!) uses the top of the line Spektrum receiver on his various turbine models. Nice that the receiver has dual battery inputs, eliminating the need for the Powerbox or similar type of system.

LiFe is 3.6v per cell not the 4.2v per cell of the LiPo batteries. the LiFe quickly drops and holds around 3.3v/cell and that is PERFECT voltage for our receivers since a 2s pack will be right at 6.6v almost exactly that of a 5 cell NiCad/NiMh pack.

So the huge advantage is the pack needs no regulator*!

Cool eh?

* = no regulator if your servo's can handle that voltage, most will but a few do not.

Mike

LiFe or 2300 Mah A123 battery. A few months ago, I was testing an A123 pack with an adaptor plug that had bare alligator clips on the end. You guessed it, el-dumbo shorted those two alligator clips together. The A123 battery pack responded by MELTING the copper servo wire right out of the wires insulation. I could swear that A123 pack was laughing at me when the smoke cleared.

That pack was completely undamaged, you can pull more than 30 amps out them without issues.

One of our old club members (Been flying RC since 1959!) uses the top of the line Spektrum receiver on his various turbine models. Nice that the receiver has dual battery inputs, eliminating the need for the Powerbox or similar type of system.

Dual power input RX solves one of the issues folks go to a Powerbox for - not all of them. If you get into GS planes like my buddy's 42% Giles - you have (3) servos per aileron, 2 for the elevators, THREE on the rudder . But it does help with power redundancy

Only other plane I show with any kind of redundancy (according to the spreadsheet I made anyway - my memory is too full of full scale right now) is my 50cc Ultimate Biplane. AR9000, have (1) A123 fed to both the BATT and AUX4 port via a Y harness, plus a DCUP fed into AUX3. Built this right when all the panic over Spektrum brownouts started - didn't want to take any chances.

Jeff/LAX
(don't panic - I don't land the planes)
(but I've been known to lie.....)

Dual power input RX solves one of the issues folks go to a Powerbox for - not all of them. If you get into GS planes like my buddy's 42% Giles - you have (3) servos per aileron, 2 for the elevators, THREE on the rudder . But it does help with power redundancy.

Yup, in an earlier posting, one of my club members has a model with FOUR servos on the rudder alone. That model uses one of those powerboxes to handle the maize of servo connectors, what with rudder, elevators, ailerons, and flaps.

I think he has more in servos in that model than my $1000 Extra 330's total cost.

Had I started the 36% plane new - I'd have probably gone the powerbox route. As it was, there was a guy on FG that had the plane basically bind and fly (I just cloned his 9303 program), and it was flying fine without one. Only thing I did was put a pair of new A123's in her, rework the CG, fuel up and fly.

Jeff/LAX
(don't panic - I don't land the planes)
(but I've been known to lie.....)

Would that be a dual battery setup with TWO two cell 2300 mah A123's as a primary/backup? Or a single two cell A123 2300 Mah battery?

IMHO, any of these larger model airplanes should have dual batteries for the receiver, just in case.

As for the powerbox, if you've got enough connections on the receiver, guess the powerbox simply is not needed???

You need the power box or you have to construct something similar. Put the servo bus (both positive and negative leads) on a separate bus and disconnect the positive servo leads from the receiver and connect them to the servo bus. You still need the signal leads and ground leads from the receiver to the servos. i.e. the servo bus ground lead and the receiver ground leads must be connected together.

You need the power box or you have to construct something similar. Put the servo bus (both positive and negative leads) on a separate bus and disconnect the positive servo leads from the receiver and connect them to the servo bus. You still need the signal leads and ground leads from the receiver to the servos. i.e. the servo bus ground lead and the receiver ground leads must be connected together.

Nope, I don't have an "E" after my name, just 46 years as a senior electronic tech.

I've worked with a lot of the better Electrical Engineers in the business during that time, and unfortunately worked with one of the dumbest of all time. One production supervisor told me that Engineer NEVER designed anything that worked, or was manufacturable.

On something like this, of critical importance, it might be a good idea to go the Powerbox, or similar configuration. That is something that has been designed, and fully tested for model airplane application.

This could be built up from scratch, but it would be best to lay out a circuit board for optimum reliability.